1. A substantial fraction of successful exits are now acquisitions. If you have ever been a part of an acquisition you know that unless the acquired company is a unicorn it is unlikely that you will see anything unless you are a key member of personnel. I've seen this happen to friends at >100 companies.
2. Long timelines to public complicate things. Options, even on a 10 year timeline, may expire before you can reasonably exercise them. The lack of cash can hinder life plans (children, house) and incentivise you to bet big. Each round requires the org to once again execute. If I build play a key role in making a business worth 100 million, and we raise at a value of 2 billion and fail to get there, my stock might now be worth very little.
The E(V) at larger companies is awesome by comparison.